The present invention relates to an active safety device that detects an obstacle such as a step on the ground, and informs a driver of the presence of the obstacle or controls a vehicle so as not to approach the obstacle when there is a risk of run off or collision, and to a method of estimating a relative position between the vehicle and the obstacle when a sensor can detect only a range remote from the vehicle and cannot detect an obstacle on the ground near the vehicle.
An active safety device that can respond to a low obstacle such as a step on the ground is disclosed, for example, in JP-A-2005-128722. Such a device scans front of a vehicle with a two-dimensional laser radar to recognize and store an obstacle during traveling, and simultaneously calculates and stores an amount of traveling of the vehicle from a rotational speed of drive wheels. A position of an obstacle determined to be placed outside a detection area after detection is estimated from information on a position of the obstacle at the time of detection and an amount of traveling of the vehicle. A collision between the vehicle and the obstacle is predicted from the detected or estimated position of the obstacle, and when the collision is predicted, a traveling state is corrected so as to prevent the collision. In this manner, a collision with an obstacle even in a dead angle of the laser is avoided.
However, the method of calculating the amount of traveling of the vehicle from the rotational speed of the drive wheels as disclosed in JP-A-2005-128722 cannot measure a lateral velocity of the vehicle though can measure a fore/aft velocity and a yaw angular velocity. The lateral velocity is lower than the fore/aft velocity, but the calculation of the amount of traveling of the vehicle includes an error without measurement or estimation of the lateral velocity. Particularly, the error increases as a range detectable by a sensor is more remote from the vehicle, thereby preventing precise prediction of a collision. Also, as vehicle speed increases, a sideslip angle of the vehicle increases and an amount of lateral movement increases. Therefore, it becomes impossible to effect precise prediction of a collision as vehicle speed increases.